Reduced-complexity antenna system using multiplexed receive chain processing

ABSTRACT

A method and associated system for processing a plurality of replicas of a signal in a signal processing chain, the method includes receiving each of the plurality of replicas of the signal at one of a corresponding plurality of respective antenna elements and orthogonally multiplexing the replicas of the signal on to a single processing chain. The multiplexed replicas are down converted from RF to baseband and converted from an analog to a digital multiplexed signal. The digital multiplexed replicas are then demultiplexed into a plurality of separate signals that correspond to replicas of the signal received at respective ones of the plurality of antennas. In variations, the orthogonal multiplexing includes frequency spreading the replicas of the signal on the single processing chain in accordance with complex Walsh codes. In other variations, the signal replicas are offset in phase by 90 degrees and time multiplexed on the single processing chain.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority under 35 U.S.C. §119(e) to U.S.Provisional Application No. 60/391,347 entitled REDUCED-COMPLEXITYANTENNA SYSTEM USING MULTIPLEXED RECEIVE CHAIN PROCESSING, filed Jun.24, 2002, which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to an antenna diversity receiverfor radio communication systems, and more particularly to areduced-complexity antenna arrangement disposed to utilize a singleprocessing chain of the associated diversity receiver.

[0004] 2. Background Information

[0005] It has recently been proposed that both the performance andcapacity of existing wireless system could be improved through the useof so-called “smart” antenna techniques. In particular, it has beensuggested that such techniques, coupled with space-time signalprocessing, could be utilized both to combat the deleterious effects ofmultipath fading of a desired incoming signal and to suppressinterfering signals. In this way both performance and capacity ofdigital wireless systems in existence or being deployed (e.g.,CDMA-based systems, TDMA-based systems, WLAN systems, and OFDM-basedsystems such as IEEE 802.11a/g) may be improved.

[0006] It is anticipated that smart antenna techniques will beincreasingly utilized both in connection with deployment of base stationinfrastructure and mobile subscriber units (e.g, handsets) in cellularsystems in order to address the increasing demands being placed uponsuch systems. These demands are arising in part from the shift underwayfrom current voice-based services to next-generation wireless multimediaservices and the accompanying blurring of distinctions among voice,video and data modes of transmission. Subscriber units utilized in suchnext-generation systems will likely be required to demonstrate highervoice quality relative to existing cellular mobile radio standards aswell as to provide high-speed data services (e.g., as high as 10Mbits/s). Achieving high speed and high quality of service, however, iscomplicated because it is desireable for mobile subscriber units to besmall and lightweight, and to be capable of reliably operating in avariety of environments (e.g., cellular/microcellular/picocellular,urban/suburban/rural and indoor/outdoor). Moreover, in addition tooffering higher-quality communication and coverage, next-generationsystems are desired to more efficiently use available bandwidth and tobe priced affordably to ensure widespread market adoption.

[0007] In many wireless systems, three principal factors tend to accountfor the bulk of performance and capacity degradation: multipath fading,delay spread between received multipath signal components, andco-channel interference (CCI). As is known, multipath fading is causedby the multiple paths which may be traversed by a transmitted signal enroute to a receive antenna. The signals from these paths add togetherwith different phases, resulting in a received signal amplitude andphase that vary with antenna location, direction and polarization, aswell as with time (as a result of movement through the environment).Increasing the quality or reducing the effective error rate in order toobviate the effects of multipath fading has proven to be extremelydifficult. Although it would be theoretically possible to reduce theeffects of multipath fading through use of higher transmit power oradditional bandwidth, these approaches are often inconsistent with therequirements of next-generation systems.

[0008] As mentioned above, the “delay spread” or difference inpropagation delays among the multiple components of received multipathsignals has also tended to constitute a principal impediment to improvedcapacity and performance in wireless communication systems. It has beenreported that when the delay spread exceeds approximately ten percent(10%) of the symbol duration, the resulting significant intersymbolinterference (ISI) generally limits the maximum data rate. This type ofdifficulty has tended to arise most frequently in narrowband systemssuch as the Global System for Mobile Communication (GSM).

[0009] The existence of co-channel interference (CCI) also adverselyaffects the performance and capacity of cellular systems. Existingcellular systems operate by dividing the available frequency channelsinto channel sets, using one channel set per cell, with frequency reuse.Most time division multiple access (TDMA) systems use a frequency reusefactor of 7, while most code division multiple (CDMA) systems use afrequency reuse factor of 1. This frequency reuse results in CCI, whichincreases as the number of channel sets decreases (i.e., as the capacityof each cell increases). In TDMA systems, the CCI is predominantly fromone or two other users, while in CDMA systems there may exist manystrong interferers both within the cell and from adjacent cells. For agiven level of CCI, capacity can be increased by shrinking the cellsize, but at the cost of additional base stations.

[0010] The impairments to the performance of cellular systems of thetype described above may be at least partially ameliorated by usingmulti-element antenna systems designed to introduce a diversity gaininto the signal reception process. There exist at least three primarymethods of effecting such a diversity gain through decorrelation of thesignals received at each antenna element: spatial diversity,polarization diversity and angle diversity. In order to realize spatialdiversity, the antenna elements are sufficiently separated to enable lowfading correlation. The required separation depends on the angularspread, which is the angle over which the signal arrives at the receiveantennas.

[0011] In the case of mobile subscriber units (e.g, handsets) surroundedby other scattering objects, an antenna spacing of only one quarterwavelength is often sufficient to achieve low fading correlation. Thispermits multiple spatial diversity antennas to be incorporated within ahandset, particularly at higher frequencies (owing to the reduction inantenna size as a function of increasing frequency). Furthermore, dualpolarization antennas can be placed close together, with low fadingcorrelation, as can antennas with different patterns (for angle ordirection diversity). However, each antenna element deployed in awireless handset requires a separate chain of signal processingelectronics, which increases the cost and power consumption of thehandset.

SUMMARY OF THE INVENTION

[0012] In one embodiment, the invention can be characterized as amethod, and means for accomplishing the method, of receiving a signal,the method including the steps of: receiving each of a plurality ofreplicas by one of a corresponding plurality of antenna elements so asto thereby generate a plurality of received signal replicas;orthogonally multiplexing the plurality of received signal replicas intoa multiplexed signal provided to a single processing chain; andtransforming, within the single processing chain, the multiplexed signalinto a plurality of separate signals that each corresponds to one of thereplicas of the signal.

[0013] In variations, orthogonal multiplexing is carried out accordingto a complex Walsh coding scheme. In other variations, respectiveswitching signals to multiplex the signal replicas are offset from eachother by 90 degrees.

[0014] In another embodiment the invention can be characterized as amethod for receiving a signal including the steps of: receiving each ofa multiplicity of replicas of the signal by one of a correspondingmultiplicity of antenna elements so as to thereby generate amultiplicity of received signal replicas; switching signal energy fromamong ones of a first subset of the multiplicity of antenna elements tocreate a first signal comprising signal energy from each of the ones ofthe first subset of the multiplicity of antenna elements; switchingsignal energy from among ones of a second subset of the multiplicity ofantenna elements to create a second signal comprising signal energy fromeach of the ones of the second subset of the multiplicity of antennaelements; offsetting, in phase, the second signal from the first signal;combining the second signal with the first signal thereby forming amultiplexed signal comprising information representative of eachrespective replica of the signal; and transforming, within the singleprocessing chain, the multiplexed signal into separate signals whereineach of the separate signals corresponds to one of the replicas of thesignal.

[0015] In a further embodiment, the invention can be characterized as anapparatus for receiving a signal, the apparatus comprising: a pluralityof antenna elements spatially arranged to receive one of a correspondingplurality of replicas of the signal so as to be capable of generating aplurality of received signal replicas; a signal processing chain; and anorthogonal multiplexer, coupled between the plurality of antennaelements and the signal processing chain, wherein the orthogonalmultiplexor is configured to receive the plurality of received signalreplicas and orthogonally multiplex the plurality of received signalreplicas as a multiplexed signal on to the signal processing chain. Thesignal processing chain includes a demultiplexer configured to transformthe multiplexed signal into a plurality of separate signals, whereineach of the plurality of separate signals corresponds to one of thereplicas of the signal.

[0016] In yet another embodiment, the invention may be characterized asa method for orthogonally multiplexing a signal, the method comprisingsteps of: generating a plurality of orthogonal signals; multiplying eachof the plurality of orthogonal signals by one of a correspondingplurality of replicas of the signal so as to thereby generate aplurality of coded signal replicas, wherein each of the plurality ofreplicas of the signal is received by one of a corresponding pluralityof antenna elements; and combining the plurality of coded signalreplicas to form a orthogonally multiplexed signal.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In the accompanying drawings:

[0018]FIG. 1 is a block diagram of a conventional diversity receiver inwhich the signals received by multiple antenna elements are weighted andcombined in order to generate an output signal;

[0019]FIG. 2 is a block diagram of a conventional spatial-temporal (ST)filtering arrangement;

[0020]FIG. 3 is a representation of a multiple-input/multiple-outputantenna arrangement within a wireless communication system;

[0021]FIG. 4 is a block diagram depicting a conventional architecture ofa multiple receive antenna system in the RF domain;

[0022]FIG. 5 is a block diagram representing a digital equivalent to thecircuit of FIG. 4;

[0023]FIG. 6 is a block diagram of a plural-element antenna processingmodule in accordance with one embodiment of the present invention;

[0024]FIG. 7 is a flow chart depicting steps traversed by theplural-element antenna processing module of FIG. 6 when receiving asignal according to one embodiment of the present invention;

[0025]FIGS. 8A and 8B are graphs illustratively representing an outputof the multiplexing switch of the plural-element antenna processingmodule of FIG. 6 in both the time domain and the frequency domainrespectively according to one embodiment;

[0026]FIG. 9 is a graph representing a signal waveform appearing at theoutput of the multiplexing switch of the plural-element antennaprocessing module of FIG. 6 according to one embodiment;

[0027]FIG. 10 is a graph depicting an output of one of the low-passfilters of the plural-element antenna processing module of FIG. 6 whenthe switching tone and a next harmonic are admitted;

[0028]FIG. 11 is a graph depicting an output of one of the low-passfilters of the plural-element antenna processing module of FIG. 6 whenonly the fundamental switching tone is admitted;

[0029]FIGS. 12A and 12B are graphs depicting the pulse shape of anexemplary implementation of the matched filters of the plural-elementantenna processing module of FIG. 6 in the time and frequency domainrespectively;

[0030]FIGS. 13A and 13B are graphs depicting an output of the matchedfilters of the plural-element antenna processing module of FIG. 6 in thetime and frequency domain respectively;

[0031]FIG. 14 is a graph depicting a constellation estimate whenswitching of the plural-element antenna processing module of FIG. 6 iscarried out at five switching operations per symbol;

[0032]FIG. 15 is a graph depicting another constellation estimate whenswitching of the plural-element antenna processing module of FIG. 6 iscarried out at twenty switching operations per symbol;

[0033]FIG. 16 is a graph depicting yet another constellation estimatewhen switching of the plural-element antenna processing module of FIG. 6is carried out at fifty switching operations per symbol;

[0034]FIG. 17 is a graph depicting an average bit error rate for asingle antenna system;

[0035]FIG. 18 is a graph depicting an average bit error rate for theantenna processing module of FIG. 6 operative at a switching frequencyfs of twenty times (20×) the applicable symbol rate;

[0036]FIG. 19 is a graph depicting an average bit error rate for theantenna processing module of FIG. 6 operative at a switching frequencyfs of two times (2×) the applicable symbol rate;

[0037]FIG. 20 is another embodiment of an antenna processing moduleconfigured to operate with more than two antenna elements;

[0038]FIG. 21 is a flow chart depicting steps traversed by theplural-element antenna processing module of FIG. 20 when receiving asignal according to one embodiment of the present invention;

[0039]FIG. 22 is a timing diagram of switching signals applied to two ofthe antenna elements of FIGS. 6 and 21 according to one embodiment;

[0040]FIG. 23 is a timing diagram of switching signals applied to two ofthe antenna elements of FIGS. 6 and 21 according to one embodiment;

[0041]FIG. 24 is yet another embodiment of an antenna-processing moduleconfigured to operate with more than two antenna elements;

[0042]FIGS. 25A and 25B are a complex Walsh coding matrix and associatedtiming diagram, according to one embodiment, utilized to provideswitching signals to the mixers of the antenna-processing module of FIG.24; and

[0043]FIGS. 26A and 26B are a complex Walsh coding matrix and associatedtiming diagram, according to another embodiment embodiment, utilized toprovide switching signals to the mixers of the antenna-processing moduleof FIG. 24.

DETAILED DESCRIPTION OF THE INVENTION

[0044] In the following description, various aspects of the presentinvention will be described. However, it will be apparent to thoseskilled in the art that the present invention may be practiced with onlysome or all aspects of the present invention. For purposes ofexplanation, specific numbers, materials and configurations are setforth in order to provide a thorough understanding of the presentinvention. However, it will also be apparent to one skilled in the artthat the present invention may be practiced without the specificdetails. In other instances, well known features are omitted orsimplified in order not to obscure the present invention.

[0045] Various operations will be described as multiple discrete stepsperformed in turn in a manner that is most helpful in understanding thepresent invention, however, the order of description should not beconstrued as to imply that these operations are necessarily orderdependent, in particular, the order the steps are presented.Furthermore, the phrase “in one embodiment” will be used repeatedly,however the phrase does not necessarily refer to the same embodiment,although it may.

[0046] In order to configure a mobile device to process signals frommultiple antenna elements, the cost and power consumption of theassociated electronics within the device should desirably be capable ofimplementation in a cost-effective manner. In this regard the presentinvention is directed to a system and method for implementing multipleantenna elements within mobile devices in a manner that potentiallyreduces costs, which typically accompany multi-element antennaarrangements. The present invention is not limited to mobile devices andmay also be applied to infrastructure elements (e.g., base stations andaccess points). In addition, the present invention is applicable tonearly all known wireless standards and modulation schemes (e.g., GSM,CDMA2000, WCDMA, WLAN, fixed wireless standards, OFDM and CDMA). As willbe described below, various advantages offered by the present inventionderive from the multiplexing of the signals received from a number ofantenna elements onto a common receive chain processing path in order toreduce overall power consumption and cost.

[0047] For example, the present invention according to severalembodiments provides a reduced-complexity, plural-element antennaarrangement and associated receiver design capable of being implementedat low cost. In some embodiments, the antenna arrangement and receiverdesign does not materially increase power consumption relative tosingle-element approaches, thereby rendering it particularly suitablefor implementation within wireless handsets.

[0048] In accordance with one aspect of the invention, samples fromplural antenna elements are time-multiplexed onto a single RF processingpath using orthogonal switching functions. Demultiplexing is thenperformed in the digital domain along with channel selection and spatialand time processing.

[0049] In order to facilitate appreciation of the principals of theinvention, a brief overview of various conventional multi-elementantenna systems designed to mitigate delay spread, interference andfading effects is provided with reference to FIGS. 1-4.

[0050] Referring first to FIG. 1, shown is a block diagram of aconventional diversity receiver 100 in which the signals received bymultiple antenna elements are weighted and combined in order to generatean output signal. Shown in the conventional diversity receiver 100 are acollection of M antenna elements 102, and coupled with each respectiveantenna element are parallel receive chains 104, 106, 108 that includerespective weighting portions 110, 112, 114. The receive chains 104,106, 108 all couple with a combiner 116 and a combined single 118 exitsfrom the combiner 116.

[0051] With M antenna elements, such an array generally provides anincreased antenna gain of “M” as well as a diversity gain againstmultipath fading dependent upon the correlation of the fading among theantenna elements. In this context the antenna gain is defined as thereduction in required receive signal power for a given average outputsignal-to-noise ratio (SNR), while the diversity gain is defined as thereduction in the required average output SNR for a given bit error rate(BER) with fading.

[0052] For interference mitigation, each of the M antenna elements 102are weighted at the respective weighting portions 110, 112, 114 andcombined in the combiner 116 to maximizesignal-to-interference-plus-noise ratio (SINR). This weighting processis usually implemented in a manner that minimizes mean squared error(MMSE), and utilizes the correlation of the interference to reduce theinterference power.

[0053] Turning now to FIG. 2, a block diagram is shown of a conventionalspatial-temporal (ST) filtering arrangement 200. Shown are a firstantenna 202 and a second antenna 204 respectively coupled to a firstlinear equalizer 206 and a second linear equalizer 208. Outputs of eachof the first and second linear equalizers 206, 208 are coupled to acombiner 210, and an output of the combiner 201 is coupled to anMLSE/DFE portion 212.

[0054] The filtering arrangement of FIG. 2 is designed to eliminatedelay spread using joint space-time processing. In general, since theCCI is unknown at the receiver, optimum space-time (ST) equalizers,either in the sense of a minimum mean square error (MMSE) or maximumsignal-to-interference-plus-noise ratio (SINR), typically include awhitening filter, e.g. linear equalizers (LE) 206, 208 that whitens theCCI both spatially and temporally, and the filtering arrangement of FIG.2 is typical of such systems. As shown in FIG. 2, the linear equalizers(LE) 206, 208 are followed by a non-linear filter that is represented bythe MLSE/DFE portion 212, which is implemented using either a decisionfeedback equalizer (DFE) or maximum-likelihood sequence estimator(MLSE).

[0055] As is known to one of ordinary skill in the art, the turboprinciple can also be used to replace the non-linear filters withsuperior performance, but higher computational complexity. Using STprocessing (STP) techniques, SNR gains of up to 4 dB and SINR gains ofup to 21 dB has been reported with a modest number of antenna elements.

[0056] Referring next to FIG. 3, shown is a generic representation of amultiple-input/multiple-output antenna arrangement within a wirelesscommunication system. Shown are a transmitter (TX) 302 coupled tomultiple transmit antennas 304, and the multiple transmitter antennas304 are shown transmitting a signal via time varying obstructions 306 tomultiple receive antennas 308 that are coupled to a receiver (RX) 310.As shown, multiple antenna elements are deployed at both the transmitter(TX) 302 and receiver (RX) 310 of the wireless communication system.

[0057] In addition to multiple-input/multiple-output antenna (MIMO)arrangements, other antenna arrangements may be categorized, based uponthe number of “inputs” and “outputs” to the channel linking atransmitter and receiver, as follows:

[0058] Single-input/single-output (SISO) systems, which includetransceivers (e.g., mobile units and a base station) with a singleantenna for uplink and down link communications.

[0059] Multi-input/single-output (MISO) systems, which include one ormore receivers, which downlink via multiple antenna inputs, and one ormore transmitters, which uplink via a single antenna output.

[0060] Single-input/multi-output (SIMO) systems, which include one ormore receivers, which downlink via a single antenna input, and one ormore transmitters, which uplink via multiple antenna outputs.

[0061] One aspect of the attractiveness of multi-element antennaarrangements, particularly MIMOs, resides in the significant systemcapacity enhancements that can be achieved using these configurations.Assuming perfect estimates of the applicable channel at both thetransmitter and receiver are available, in a MIMO system with M receiveantennas the received signal decomposes to M independent channels. Thisresults in an M-fold capacity increase relative to SISO systems. For afixed overall transmitted power, the capacity offered by MIMOs scalewith increasing SNR for a large, but practical, number of M of antennaelements.

[0062] In the particular case of fading multipath channels, it has beenfound that the use of MIMO arrangements permits capacity to be scaled bynearly M additional bits/cycle for each 3-dB increase in SNR. This MIMOscaling attribute is in contrast to a baseline configuration,characterized by M=1, which by Shannon's classical formula scales as onemore bit/cycle for every 3-dB of SNR increase. It is noted that thisincrease in capacity that MIMO systems afford is achieved without anyadditional bandwidth relative to the single element baselineconfiguration.

[0063] However, widespread deployment of multi-element antennaarrangements in wireless communication systems (particularly withinwireless handsets) has been hindered by the resultant increase incomplexity and associated increased power consumption, cost and size.These parameter increases result, at least in part, from a requirementin many proposed architectures that a separate receiver chain beprovided for each for each antenna element.

[0064] For example, FIG. 4 depicts one conventional architecture of amultiple receive antenna system in the RF domain. As shown, theimplementation of FIG. 4 includes a separate receive chain 402, 404, 406for each of M antenna elements, and each receive chain 402, 404, 406includes elements to perform amplification, filtering and mixing. As aconsequence, the cost of implementing a system with this architecture ishigher than a system with a single receive chain.

[0065] This approach is further disadvantageous because analog phaseshifters and variable gain amplifiers are utilized, which renders itrelatively expensive and susceptible to performance degradation as aresult of aging, temperature variation, and deviation from prescribedtolerances. In addition, because the implementation of FIG. 4 makes useof a phase relationship between the received and transmitted antennaelements (i.e., the path differential delay is maintained throughouteach receive processing chain), rigid adherence to tolerances andaccurate calibration is required in each RF processing chain.

[0066] Referring next FIG. 5, shown is a block diagram representing adigital equivalent to the circuit of FIG. 4. In general, the performanceof the digital circuit arrangement of FIG. 5 is degraded forsubstantially the same reasons as was described above with reference toFIG. 4. That is, the duplication of the entire receiver chain (i.e.,from RF to baseband) associated with each antenna element leads to anincrease in size, cost, complexity and power consumption relative tosingle antenna approaches. As a result, multi-element antennaconfigurations have heretofore been unsuitable for deployment in thehandsets and other mobile terminals used within wireless communicationsystems.

Overview and System Architecture

[0067] As is described in further detail below, several embodiments ofthe reduced-complexity antenna arrangement and receiver of the presentinvention are premised on consolidating the RF processing operationsassociated with each antenna element into a single processing chain, andin some embodiments RF processing operations are consolidated into asingle processing chain as soon as is practicable.

[0068] In some embodiments, this consolidation is achieved bymultiplexing samples from a switch element connected to a pair ofantenna elements onto a single RF processing chain. Upon completion ofthe RF processing effected by this single RF chain, the incident signalsare passed through matched filters operative to reduce the applicablesample frequency to the appropriate base band rate. Upon recovery of thesignals initially received by each antenna element in the digitaldomain, the recovered signals are then subjected to conventional spatialprocessing. The structure may be generalized for use with more than apair of antenna elements by modifying the structure of themultiplexer/demultiplexer and the sample spacing of the signal streamsprovided to the matched filters associated with each antenna element.

[0069]FIG. 6 is a block diagram, which illustratively represents areceiver front end incorporating a plural-element antenna processingmodule 600 in accordance with one embodiment of the present invention.The plural-element antenna processing module 600 includes first andsecond antenna elements 602 and 604 coupled through a multiplexer switch608 to an RF processing chain 610. While referring to FIG. 6,simultaneous reference will be made to FIG. 7, which is a flowchartillustrating steps carried out by the plural-element antenna processingmodule 600 according to one embodiment of the present invention.

[0070] In operation, the first and second antenna elements 602 and 604initially receive a signal from two spatially distinct locations. Thus,replicas of the signal are received at each of the first and secondantenna elements 602 and 604 (Step 702). In several embodiments, thereplicas received at the first and second antenna elements 602 and 604are uncorrelated replicas of the signal.

[0071] Each of the replicas of the signal received at the first andsecond antenna elements 602 and 604 are then orthogonally multiplexed onto the processing chain 610 (Step 704). In some embodiments, theorthogonal multiplexing is carried out by multiplying one replica of thesignal received (e.g., at the first antenna 602) by a first switchingsignal, and multiplying another replica of the signal received (e.g., atthe second antenna 604) by a second switching signal, which is 90degrees out of phase with the first switching signal.

[0072] Referring briefly to FIG. 23, shown are two square waves, out ofphase by 90 degrees, which are exemplary of square waves used asswitching signals to multiply received replicas of the signal receivedat the first and second antennas 602, 604 according to one embodiment.As shown in FIG. 23, each of the square waves reverses polarity duringeach cycle. It should be recognized, however, that switching-squarewaves need not reverse polarity during each cycle, but by employingsquare waves that reverse polarity during each cycle (i.e., that moreclosely resemble a sin wave), fewer harmonics are produced during themultiplexing process, and as a consequence, less rigorous filtering ofthe multiplexed signal is required.

[0073] In other embodiments, as discussed further with reference toFIGS. 24 and 25, the frequency spreading is performed in accordance withcomplex Walsh coding principals.

[0074] As one of ordinary skill in the art recognizes, the multiplexer608 may be implemented using various combinations of hardware andsoftware/firmware. In one embodiment, for example, a single-poledouble-throw (SPDT) switch is utilized in connection withfrequency-offset techniques to orthogonally multiplex replicas of asignal. Alternatively, as discussed further with respect to FIG. 24,mixers are implemented to providing switching signals to the replicas ofthe received signal.

[0075] Referring briefly to FIGS. 8A and 8B, shown are representationsof the output of the multiplexing switch 608 in both the time domain andthe frequency domain respectively for an exemplary embodiment, in whichreplicas of the signal are not phase offset and the fundamental tonerequired to implement the oscillation of the switching process is offsetfrom the carrier fc by 218 kHz. In the time domain representation ofFIG. 8A, the time-multiplexing of the signals received from the firstand second antenna elements 602, 604 upon RF processing chain 610 isevident and makes apparent that the received signals differ primarilyonly in amplitude in this example. The spreading of the signal receivedby the antenna elements 602, 604 due to the operation of themultiplexing switch 608 is made apparent by the power spectrum plot inFIG. 8B. Higher order harmonics are also apparent in the power spectrumplot of FIG. 8B, and in general only the centre frequency and each ofthese 218 kHz offsets are passed into the ADCs 634, 636.

[0076] Mathematically, multiplexing may be represented as an applicationof switching signals s1(t) and s2(t) to the signal energy r1(t) receivedby the first antenna element 602 “Ant 1” and to the signal energy r2(t)received by the second antenna element 604 “Ant 2” results in:

m(t)=r1(t)s1(t)+r2(t)s2(t)

[0077] where

[0078] s1(t)=1+cos(2πfs/2t)

[0079] s2(t)=1+cos(2πfs/2t+π)

[0080] r1(t)=sin(2πfct+p1(t))

[0081] r2(t)=sin(2πfct+p2(t))

[0082] p1(t)=base band phase process as received on Ant 1

[0083] p2(t)=base band phase process as received on Ant 2

[0084] It is noted that in the above mathematical representation a sinwaveform rather than a square waveform is utilized as the switchingfunction. As a result, calculations are simplified because of the lowerharmonic content of sinusoidal waveforms relative to square waveforms.

[0085] As previously discussed, in several embodiments, switchingsignals (e.g., square waves) that reverse polarity during each cycle areused to more closely approximate a sin waveform. This substantiallyreduces or eliminates spurious harmonic energy that is potentiallyproduced.

[0086] Returning again to the mathematical representation, an expansionof m(t) yields:m(t) = r1(t) + r2(t) +   sin (2  π(fc − fs/2)t + p1(t))/2 +   sin (2  π(fc − fs/2 + π)t + p2(t))/2 +   sin (2  π(fc + fs/2)t + p1(t))/2 +   sin (2  π(fc + fs/2 + π)t + p2(t))/2

[0087] The spectrum of the signal m(t) appears as a centre peak at thecarrier frequency fc, and has identical side lobes offset by fs/2 oneither side of fc.

[0088] In one exemplary embodiment, the multiplexer 608 switches at arate of at least twenty (20) times the symbol rate of the informationreceived by the antenna elements 602 and 604. However, in alternateembodiments, the switching rate of the orthogonal multiplexor 608 rangesfrom approximately twice the applicable symbol rate to larger than 20times such rate.

[0089] Next, the multiplexed signal from the multiplexer 608 is downconverted from RF frequency (Step 706). On of ordinary skill in the artwill recognize that a single one of the side lobes discussed abovecontains the sum of the two signals of interest with a phase offset of πradians, and one side lobe reduces the applicable expression to the sumof two sinusoids offset in phase:

sin(2π(fc−fs/2)t+p1(t)/2+sin(2π(fc−fs/2+π)t+p2(t))/2

[0090] When p1(t)=p2(t), however, then this component is zero and is notof practical utility. Thus, in several embodiments, because m(t) is thesignal of interest, the received signal energy is mixed down at thecarrier frequency.

[0091] In one embodiment, as shown in FIG. 6 for example, the RFprocessing chain 610 includes an in-phase (I) branch 614 and aquadrature-phase (Q) branch 618 which respectively include a first mixerdevice 620 and a second mixer device 624. As shown, the first mixerdevice 620 is supplied with a mixing signal cos(fc), where fc denotesthe frequency of the received carrier signal. Similarly, the secondmixer device 624 is supplied with the mixing signal sin(fc). The mixerdevices 620 and 624 function to mix down the received signal energy atthe carrier frequency fc, which results in generation of a center peakat DC and a pair of side lobes “folded” on top of each other at the onehalf of the switching frequency (fs/2) of the multiplexing switch 608.

[0092] As shown in FIG. 6, the signal energy from the first mixer device620 and the second mixer device 624 is provided to a first low-passfilter 630 and a second low-pass filter 632 respectively, and in oneembodiment, the signal energy in both the in-phase (I) branch 614 andthe quadrature-phase (Q) branch 618 is filtered at a cut-off of fs.

[0093] After low pass filtering at a cut-off of fs (which leaves s1(t)and s2(t) intact), the I and Q components of m(t) are obtained asfollows: $\begin{matrix}{{{{m\_ b}{\_ I}(t)} = {{m(t)}*{\cos ( {2\quad \pi \quad {fc}\quad t} )}}}\quad} \\{\quad {= {{{s1}(t){{r1}(t)}{\cos ( {2\quad \pi \quad {fc}\quad t} )}} + {{{s2}(t)}{{r2}(t)}{\cos ( {2\quad \pi \quad {fc}\quad t} )}}}}} \\{\quad {= {{{{s1}(t)}{\sin ( {{p1}(t)} )}} + {{{s2}(t)}{\sin ( {{p2}(t)} )}}}}} \\{{{{m\_ b}{\_ Q}(t)} = {{m(t)}*{\sin ( {2\quad \pi \quad {fc}\quad t} )}}}\quad} \\{\quad {= {{{s1}(t){{r1}(t)}{\sin ( {2\quad \pi \quad {fc}\quad t} )}} + {{{s2}(t)}{{r2}(t)}{\sin ( {2\quad \pi \quad {fc}\quad t} )}}}}} \\{\quad {= {{{{s1}(t)}{\cos ( {{p1}(t)} )}} + {{{s2}(t)}{\cos ( {{p2}(t)} )}}}}}\end{matrix}$

[0094] These results are desirable because the function s1(t) and s2(t)may be regarded as being of square form.

[0095]FIGS. 9-11 provide exemplary representations of various signalsexisting proximate the low-pass filters 630 and 632. Specifically, FIG.9 represents a signal waveform appearing at the output of themultiplexing switch 608 prior to filtering by one of the low-passfilters 630 and 632.

[0096]FIG. 10 depicts the output of one of the low-pass filters 630 and632 in the case where the switching tone and the next harmonic areadmitted.

[0097] In contrast, FIG. 11 represents the signal appearing at theoutput of one of the low-pass filters in the case where only thefundamental switching tone is admitted.

[0098] The filtered signals from the first and second low pass filters630 and 632 are provided to a demultiplexer 638 via a first analog todigital converter (ADC) 634 and a second ADC 636 where the filteredsignals are converted from analog to digital (Step 708). The digitalsignals from the first analog to digital converter (ADC) 634 and asecond ADC 636 are then demultiplexed by the demultiplexer 638 (Step710).

[0099] The demultiplexer 638 operates to route samples from the firstantenna element 602 to a first slot buffer 642 and from the secondantenna element 604 to a second slot buffer 644. Thus, the demultiplexor638 provides separate signals that are representative of the signalreplicas received at the first and second antenna elements 602, 604. Thebuffered samples from the first slot buffer 642 and the second slotbuffer 644 are then pulse matched filtered by a first matched filter 650and a second matched filter 654 respectively (Step 712). After pulsematched filtering, the separate signals from the first and second pulsematched filters 650, 654 are spatially processed by a spatial processingmodule 660 (Step 714). In one exemplary embodiment, the spatialprocessing module 660 executes known spatial processing algorithms inthe digital domain.

[0100]FIGS. 12A and 12B depict a pulse shape of an exemplaryimplementation of the matched filters 650, 654 in the time and frequencydomain respectively. FIGS. 13A and 13B depict the output of the matchedfilters 650, 654 in both the time and frequency domains.

[0101] In one embodiment, the pulse matched filters 650, 654 are notconfigured to take into consideration discontinuities in the separatedemultiplexed signals that are a result of the sampling of the receivedsignals r1(t) and r2(t) during the multiplexing operation effected bythe multiplexing switch 608. As the switching frequency fs increases toorders of magnitude greater than the symbol frequency of the receivedenergy, however, any losses incurred during this effective samplingprocess tend to become negligible.

[0102] For example FIGS. 14-16 depict base band constellation estimatesgenerated (in the absence of noise and interference) on the basis ofoperation at 5, 20 and 50 switching operations per symbol, respectively.As shown, as switching frequency is increased, losses due to thesampling process become negligible.

[0103] In other embodiments, the pulse matched filters 650, 654 areconfigured to take into consideration discontinuities in the separatedemultiplexed signals that are a result of the sampling of the receivedsignals r1(t) and r2(t) during the multiplexing operation. The pulsematched filters 650, 654 in these embodiments integrate the bufferedsamples from the first slot buffer 642 and the second slot buffer 644(i.e. the separate low pass signals after low pass filtering,demultiplexing and buffering) in order to gather a maximum amount ofenergy at the sampling instants. This is accomplished by the filters650, 654 being matched to the separate low pass signals as the complexconjugate of the separate low pass signals.

[0104] The signal-to-noise performance of a receiver incorporating aprocessing module, e.g., the processing module 600 configured with twoantenna elements, e.g., the first and second antenna elements 602, 604has been compared to the performance obtained using a receiver includingonly a single antenna element. In general, it has been found that thespatial diversity offered by the configuration of the present inventionyields superior results in the presence of signal fading. In the casewhere interferers having linearly independent spatial signatures are inexistence, the configuration of the present invention has been found tooffer substantial improvements in signal-to-noise performance.

[0105] Referring next to FIGS. 17-19, for example, the average errorrate is respectively depicted for the simulated cases of (i) a singleantenna, (ii) an antenna processing module 600 configured with twoantennas and operative at a switching frequency fs of twenty times (20×)the applicable symbol rate, and (iii) an antenna processing module 600configured with two antennas and operative at a switching frequency fsof two times (2×) the applicable symbol rate.

[0106] Referring next to FIG. 18, it is observed that at the moderateswitching frequency fs of 20×/symbol a significant advantage is obtainedover the single antenna case (FIG. 17). In contrast, FIG. 19 indicatesthat at a switching frequency fs of 2×/symbol, performance is degradedrelative to the case of FIG. 18. Nonetheless, the performance at an fsof 2×/symbol appears to be superior to that of the single antenna case(FIG. 17). It should be noted that appropriate design of each matchedfilter 650, 654 may substantially reduce or eliminate any difference inperformance as a function of switching frequency fs.

[0107] Referring next to FIG. 20, shown is another embodiment of anantenna-processing module 2000 configured to operate with more than twoantenna elements. As shown, the plural-element antenna processing module2000 includes a first, a second, a third and a forth antenna elements2002, 2004, 2006, 2008 coupled to a multiplexer 2001, which is coupledto an RF processing chain 2016. While referring to FIG. 20, simultaneousreference will be made to FIG. 21, which is a flowchart illustratingsteps carried out by the antenna-processing module 2000 according to oneembodiment of the present invention.

[0108] In operation, the antennas 2002, 2004, 2006, 2008 receive asignal at spatially distinct locations, and as a consequence, each ofthe antennas 2002, 2004, 2006, 2008 receives a respective replica of thesignal (Step 2102). In several embodiments, the antennas 2002, 2004,2006, 2008 are arranged so that each receives an uncorrelated replica ofthe signal.

[0109] In one embodiment, as shown in FIG. 20, the multiplexer 2001includes a first and second multiplexing switches 2010, 2012, whichoperate as single-pole double-throw (SPDT) switches. The first andsecond antennas 2002, 2004 are coupled as a first subset of the fourantennas 2002, 2004, 2006, 2008 to the first multiplexing switch 2010and the third and forth antennas 2006, 2008 are coupled as a secondsubset of the four antennas 2002, 2004, 2006, 2008 to the secondmultiplexing switch 2012.

[0110] In the present embodiment, the first multiplexing switch 2010switches between the first and second antenna elements 2002, 2004 at arate of fs/2 to create a first signal 2014 (Step 2104). Similarly, thesecond multiplexing switch 2012 switches between the third and forthantenna elements 2006, 2008 at the same rate of fs/2 to create a secondsignal 2016 (Step 2106). The second signal 2016 is then offset, inphase, from the first signal by 90 degrees (Step 2108).

[0111] Referring briefly to FIG. 22, shown are two switching signalsutilized, in one embodiment, to perform switching between the first andsecond antenna elements 2002, 2004 (and between the third and forthantenna elements 2006, 2008) to form the first and second signals 2014,2016 of FIG. 20 respectively. In this embodiment, formation of the firstsignal is carried out by multiplying a signal replica received at thefirst antenna 2002 by a first square wave and multiplying a signalreplica received at the second antenna 2004 by a second square wave thatis 180 degrees out of phase with the first square wave. The sameswitching scheme is applied to the second and third antennas to form thesecond signal, and then, as described above, the second signal 2016 isoffset by 90 degrees from the first signal.

[0112] Referring briefly to FIG. 23, shown are two switching signalsutilized in another embodiment to perform switching between the firstand second antenna elements 2002, 2004 and between the third and forthantenna elements 2006, 2008 to form the first and second signals 2014,2016 of FIG. 20 respectively. As shown in FIG. 23 the two switchingsignals square waves that are 90 degrees out of phase with each otherand both reverse polarity during each cycle.

[0113] In this embodiment, formation of the first signal is carried outby multiplying a signal replica received at the first antenna 2002 bythe first square wave and multiplying a signal replica received at thesecond antenna 2004 by the second square wave that is 90 degrees out ofphase with the first square wave. This same switching scheme applied tothe second and third antennas to form the second signal, and then thesecond signal 2016 is offset by 90 degrees from the first signal.

[0114] Next, the first and second signals 2014, 2016 are combined toform an orthogonally multiplexed signal on a processing chain 2016 (Step2110). In this way, four antenna elements are multiplexed onto a commonreceive chain within an identical bandwidth as would be employed for atwo-antenna element embodiment. As a consequence, the present embodimentcan be implemented with less cost relative to other designs.

[0115] For example, relative to a multiplexer comprising a single-polefour-throw switch configured to switch between four antennas, thepresent embodiment uses half the bandwidth, and as a consequence, thepresent embodiment is more cost effective.

[0116] The multiplexed signal is then downconverted by a mixer device2018 (Step 2112), and filtered by a low-pass filter 2020 before beingconverted from analog to digital by a digital converter 2022.

[0117] After conversion to a digital representation, the multiplexedsignal is then demultiplexed by a demultiplexor 2024 into four separatesignals that are each representative of a corresponding replica of thesignal as received at a corresponding one of the four antenna elements2002, 2004, 2006, 2008 (Step 2114). The four separate signals are thenpulse matched filtered by respective pulse matched filters 2026, 2028,2030, 2032 before being received by a spatial processing portion 2034.

[0118] Referring next to FIG. 24, shown is yet another embodiment of anantenna processing module 2400 configured to operate with more than twoantenna elements. As shown, the plural-element antenna processing module2400 includes a first, a second, a third and a forth antenna elements2402, 2404, 2406, 2408 coupled to a multiplexer 2410, which is coupledto an RF processing chain 2016.

[0119] In operation, the antennas 2402, 2404, 2406, 2408 receive asignal at spatially distinct locations. As a consequence, each of theantennas 2402, 2404, 2406, 2408 receives a respective replica of thesignal. In several embodiments, the antennas 2402, 2404, 2406, 2408 arearranged so that each receives an uncorrelated replica of the signal.

[0120] As shown in FIG. 24, the multiplexer 2410 in the presentembodiment includes a first, a second, a third and a forth mixing units2412, 2414, 2416, 2418 that are respectively coupled to the antennas2402, 2404, 2406, 2408. The mixing units 2412, 2414, 2416, 2418 operateto inject switching signals into each of the signal replicas received atthe respective antennas 2402, 2404, 2406, 2408. In several embodiments,the switching signals provided by each of the mixers are orthogonalswitching signals.

[0121] In one embodiment for example, the switching signals areimplemented according to a complex Walsh coding scheme. Referringbriefly to FIGS. 25A and 25B, for example, shown are one embodiment ofcomplex Walsh code matrix and a corresponding signal-timing diagramrespectively. It should be noted that each element in the complex codematrix of FIG. 25 is a complex number, but in the present embodiment,the imaginary component of each element is zero for sake of simplicity.It should also be noted that in the present embodiment, the elements inthe matrix are either 0 or a 1, which correspond to either an “off” or“on” state.

[0122] In operation, each row of the complex Walsh matrix isinterpreted, e.g., by a CPU (not shown) and a corresponding switchingsignal is created, as shown in FIG. 25B, that is provided to acorresponding mixing unit 2412, 2414, 2416, 2418. The mixing units 2412,2414, 2416, 2418 then mix the switching signals with the respectivereplicas received at the antennas 2402, 2404, 2406, 2408. For example,the first row of the complex Walsh matrix in FIG. 25A is 0, 0, 0, 1, andas a consequence, during a first three switching cycles, as shown inFIG. 25B, the mixer 2412 mixes an “off” signal with the signal replicareceived at the first antenna 2402.

[0123] Referring to FIGS. 26A and 26B, shown are another embodiment ofcomplex Walsh code matrix and a corresponding signal-timing diagramrespectively. As shown in FIG. 26A, the elements of the complex Walshcode matrix are either a 1 or a −1, and as a result, correspondingsignals, as shown in FIG. 26B, (in some instances) reverse polarity fromcycle to cycle. As a consequence, there are fewer harmonics producedwhen mixing the signals shown in FIG. 26B relative to the signals shownin FIG. 25B.

[0124] After the signal replicas from the antennas 2402, 2404, 2406,2408 are mixed by respective switching signals, e.g., the switchingsignals described with reference to FIGS. 25B and 26B, the coded signalreplicas 2420, 2422, 2424, 2426 are then combined by a signal combiner2428 to produce an orthogonally multiplexed signal on the processingchain 2430.

[0125] It should be noted that the orthogonal multiplexing scheme of thepresent embodiment is one embodiment of carrying out Step 704 of FIG. 7.

[0126] After multiplexing, in some embodiments, the multiplexed signalis down converted by a mixer 2430, filtered by a low pass filter 2432,converted to a digital signal by an analog to digital converter 2434 andthen demultiplexed, by a demultiplexor 2436 into four representations ofthe original signal replicas received at the antennas 2402, 2404, 2406,2408. The separate signals are then pulse match filtered by respectivepulse matched filters 2438, 2440, 2442, 2444 before being spatiallyprocessed by a spatial processing unit 2446.

[0127] The described and other embodiments could be implemented insystems including, but not limited to time division multiple access(TDMA), code division multiple access (CDMA), frequency divisionmultiple access (FDMA), orthogonal frequency division multiple access(OFDM), or any combination of these. This could also include systemsusing any type of modulation to encode the digital data.

[0128] The foregoing description, for purposes of explanation, usedspecific nomenclature to provide a thorough understanding of theinvention. However, it will be apparent to one skilled in the art thatthe specific details are not required in order to practice theinvention. In other instances, well-known circuits and devices are shownin block diagram form in order to avoid unnecessary distraction from theunderlying invention. Thus, the foregoing descriptions of specificembodiments of the present invention are presented for purposes ofillustration and description. They are not intended to be exhaustive orto limit the invention to the precise forms disclosed, obviously manymodifications and variations are possible in view of the aboveteachings. The embodiments were chosen and described in order to bestexplain the principles of the invention and its practical applications,to thereby enable others skilled in the art to best utilize theinvention and various embodiments with various modifications as aresuited to the particular use contemplated.

What is claimed is:
 1. A method for receiving a signal comprising:receiving a plurality of replicas of the signal, each of the pluralityof replicas being received by one of a corresponding plurality ofantenna elements so as to thereby generate a plurality of receivedsignal replicas; orthogonally multiplexing the plurality of receivedsignal replicas into a multiplexed signal provided to a singleprocessing chain; and transforming, within the single processing chain,the multiplexed signal into a plurality of separate signals wherein eachof the plurality of separate signals corresponds to one of the replicasof the signal.
 2. The method of claim 1 wherein the transformingincludes frequency downconverting the multiplexed signal, therebygenerating a downconverted multiplexed signal.
 3. The method of claim 2further including converting the downconverted multiplexed signal to adigital multiplexed signal.
 4. The method of claim 3 further includingdemultiplexing the digital multiplexed signal into the plurality ofseparate signals.
 5. The method of claim 1, wherein the orthogonallymultiplexing comprises frequency spreading the plurality of replicas onto the single processing chain according to an orthogonal coding scheme.6. The method of claim 5, wherein the frequency spreading is carried outaccording to a Walsh coding scheme.
 7. The method of claim 6, whereinthe frequency spreading is carried out according to a complex Walshcoding scheme.
 8. The method of claim 1, wherein the orthogonallymultiplexing comprises offsetting, by ninety degrees in phase, one ofthe plurality of replicas from another one of the plurality of replicas.9. The method of claim 8, further comprising: multiplying the other oneof the plurality of replicas by a first square wave; multiplying the oneof the plurality of replicas by a second square wave offset in phasefrom the first square wave by ninety degrees.
 10. The method of claim 9,wherein the first and second square waves reverse polarity during eachcycle.
 11. The method of claim 1, further including: pulse matchfiltering each of the separate signals.
 12. The method of claim 1,wherein the receiving includes receiving the plurality of replicas ofthe signal as uncorrelated replicas of the signal.
 13. The method ofclaim 1, wherein the orthogonally multiplexing the plurality of replicasincludes: switching between a first subset of the plurality of antennaelements to create a first signal of respective replicas of the signalfrom the first subset of the plurality of antenna elements; switchingbetween a second subset of the plurality of antenna elements to create asecond signal of respective replicas of the signal from the secondsubset of the plurality of antenna elements; offsetting, in phase, thesecond signal from the first signal; and combining the second signalwith the first signal thereby forming the multiplexed signal.
 14. Amethod for receiving a signal comprising: receiving a multiplicity ofreplicas of the signal, each of the multiplicity of replicas beingreceived by one of a corresponding multiplicity of antenna elements soas to thereby generate a multiplicity of received signal replicas;switching signal energy from among ones of a first subset of themultiplicity of antenna elements to create a first signal comprisingsignal energy from each of the ones of the first subset of themultiplicity of antenna elements; switching signal energy from amongones of a second subset of the multiplicity of antenna elements tocreate a second signal comprising signal energy from each of the ones ofthe second subset of the multiplicity of antenna elements; offsetting,in phase, the second signal from the first signal; combining the secondsignal with the first signal, thereby forming a multiplexed signalcomprising information representative of each respective replica of thesignal; and transforming, within the single processing chain, themultiplexed signal into separate signals wherein each of the separatesignals corresponds to one of the replicas of the signal.
 15. The methodof claim 14 wherein the transforming includes frequency downconvertingthe multiplexed signal, thereby generating a downconverted multiplexedsignal.
 16. The method of claim 15 further including converting thedownconverted multiplexed signal to a digital multiplexed signal. 17.The method of claim 16 further including demultiplexing the digitalmultiplexed signal into the separate signals.
 18. The method of claim14, wherein the switching signal energy from among ones of a firstsubset of the multiplicity of antenna elements includes switchingbetween a first pair of the multiplicity of antenna elements to createthe first signal, wherein the switching signal energy from among ones ofa second subset of the multiplicity of antenna elements includesswitching between a second pair of the multiplicity of antenna elementsto create the second signal.
 19. The method of claim 18, wherein theswitching between the first pair of the multiplicity of antenna elementsincludes multiplying each respective replica of the signal at each ofthe first pair of the multiplicity of antenna elements by respectivesquare waves wherein each of the respective square waves are out ofphase by 180 degrees.
 20. The method of claim 19, wherein the respectivesquare waves reverse polarity during each cycle.
 21. The method of claim18, wherein the switching between the first pair of the multiplicity ofantenna elements includes multiplying each respective replica of thesignal at each of the first pair of the multiplicity of antenna elementsby respective square waves wherein each of the respective square wavesare out of phase by 90 degrees.
 22. The method of claim 21, wherein therespective square waves reverse polarity during each cycle.
 23. Anapparatus for receiving a signal comprising: a plurality of antennaelements, wherein the plurality of antenna elements are spatiallyarranged to receive one of a corresponding plurality of replicas of thesignal so as to be capable of generating a plurality of received signalreplicas; a signal processing chain; and an orthogonal multiplexer,coupled between the plurality of antenna elements and the signalprocessing chain, wherein the orthogonal multiplexor is configured toreceive the plurality of received signal replicas and orthogonallymultiplex the plurality of received signal replicas as a multiplexedsignal on to the signal processing chain; wherein the signal processingchain includes a demultiplexer configured to transform the multiplexedsignal into a plurality of separate signals, wherein each of theplurality of separate signals corresponds to one of the replicas of thesignal.
 24. The apparatus of claim 23, wherein the orthogonalmultiplexer includes: a first switch coupled to a first subset of theplurality of antenna elements wherein the first switch is configured toswitch between a first subset of the plurality of antenna elements tocreate, at an output of the first switch, a first signal of respectivereplicas of the signal from the first subset of the plurality of antennaelements; a second switch coupled to a second subset of the plurality ofantenna elements wherein the second switch is configured to switchbetween a second subset of the plurality of antenna elements to create,at an output of the second switch, a second signal of respectivereplicas of the signal from the second subset of the plurality ofantenna elements; a phase offsetting portion coupled to the output ofthe second switch wherein the phase offsetting portion is configured togenerate, at an offsetting output, an offset signal wherein the offsetsignal is offset in phase from the first signal; and a signal combinercoupled to the output of the first switch and the offsetting output andconfigured to receive and combine the first signal and the offset signalto form the multiplexed signal on the signal processing chain.
 25. Theapparatus of claim 24, wherein the first and second switches aresingle-pole double-throw switches.
 26. The apparatus of claim 23,wherein the orthogonal multiplexer comprises: a plurality of mixersconfigured to provided a plurality of mixed signals, wherein each of theplurality of mixers is coupled to one of the plurality of antennaelements, wherein each mixer is configured to generate one of theplurality of mixed signals by mixing one of a plurality of orthogonalswitching signals with the one of the corresponding plurality ofreplicas of the signal received at each of the plurality of antennaelements; and a combiner coupled the plurality of mixers and configuredto receive and combine the plurality of mixed signals thereby formingthe multiplexed signal.
 27. The apparatus of claim 23 wherein the signalprocessing chain includes: a downconverting mixer coupled to theorthogonal mixer, wherein the downconverting mixer is configured todownconvert the multiplexed signal into a downconverted multiplexedsignal.
 28. The apparatus of claim 27 wherein the signal processingchain includes: an analog to digital converter coupled to thedownconverting mixer wherein the analog to digital converter isconfigured to convert the downconverted multiplexed signal into adigital multiplexed signal, wherein the demultiplexer is configured totransform the digital multiplexed signal into the plurality of separatesignals.
 29. An apparatus for receiving a signal comprising: means forreceiving a plurality of replicas of the signal; a signal processingchain; means for orthogonally multiplexing the plurality of receivedsignal replicas into a multiplexed signal provided to the signalprocessing chain; and means for transforming, within the signalprocessing chain, the multiplexed signal into a plurality of separatesignals wherein each of the plurality of separate signals corresponds toone of the replicas of the signal.
 30. The apparatus of claim 29 whereinthe means for transforming includes means for frequency downconvertingthe multiplexed signal into a downconverted multiplexed signal.
 31. Theapparatus of claim 30 further including means for converting thedownconverted multiplexed into a digital multiplexed signal.
 32. Theapparatus of claim 31 further including means for demultiplexing thedigital multiplexed signal into the plurality of separate signals. 33.The apparatus of claim 29, wherein the means for orthogonallymultiplexing comprises means for frequency spreading the plurality ofreplicas on to the signal processing chain according to an orthogonalcoding scheme.
 34. The apparatus of claim 33, wherein the means forfrequency spreading comprises means for carrying out frequency spreadingaccording to a Walsh coding scheme.
 35. The apparatus of claim 34,wherein the means for frequency spreading comprises means for carryingout the frequency spreading according to a complex Walsh coding scheme.36. The apparatus of claim 29, wherein the means for orthogonallymultiplexing comprises means for offsetting, by ninety degrees in phase,one of the plurality of replicas from another one of the plurality ofreplicas.
 37. The apparatus of claim 36, further comprising: means formultiplying the other one of the plurality of replicas by a first squarewave; and means for multiplying the one of the plurality of replicas bya second square wave offset in phase from the first square wave byninety degrees.
 38. The apparatus of claim 37, wherein the means formultiplying the other one and the means for multiplying the one includerespective means for multiplying the other one and the one of theplurality of replicas by the first square wave first and second squarewaves wherein the first and second square waves reverse polarity duringeach cycle.
 39. The apparatus of claim 29, further including: means forpulse match filtering each of the separate signals.
 40. The apparatus ofclaim 29, wherein the means for receiving includes means for receivingthe plurality of replicas of the signal as uncorrelated replicas of thesignal.
 41. The apparatus of claim 29, wherein the means fororthogonally multiplexing the plurality of replicas includes: means forswitching between a first subset of the plurality of antenna elements tocreate a first signal of respective replicas of the signal from thefirst subset of the plurality of antenna elements; means for switchingbetween a second subset of the plurality of antenna elements to create asecond signal of respective replicas of the signal from the secondsubset of the plurality of antenna elements; means for offsetting, inphase, the second signal from the first signal; and means for combiningthe second signal with the first signal thereby forming the multiplexedsignal.
 42. A method for orthogonally multiplexing a signal comprising:generating a plurality of orthogonal signals; multiplying each of theplurality of orthogonal signals by one of a corresponding plurality ofreplicas of the signal so as to thereby generate a plurality of codedsignal replicas, wherein each of the plurality of replicas of the signalis received by one of a corresponding plurality of antenna elements; andcombining the plurality of coded signal replicas to form an orthogonallymultiplexed signal.
 43. The method of claim 42, wherein the generatingincludes generating the plurality of orthogonal signals according to aWalsh coding scheme.
 44. The method of claim 42, wherein the generatingincludes generating at least two of the orthogonal signals as orthogonalsignals that reverse polarity during each cycle.
 45. The method of claim1, wherein the signal complies with a communication protocol selectedfrom the group consisting of: orthogonal frequency division multiplexing(OFDM), time division multiple access (TDMA), code division multipleaccess (CDMA), gaussian minimum shift keying (GMSK), complementary codekeying (CCK), quadrature phase shift keying (QPSK), frequency shiftkeying (FSK), phase shift keying (PSK), and quadrature amplitudemodulation (QAM).